This invention relates in general to gas measuring apparatus and in particular to a new and useful device for determining whether the apparatus is functioning properly.
In gas measuring devices, such as gas detectors equipped with conventional gas indicator tubes which are filled with reagents, the air to be tested is frequently directed through the tube for a long period of time either by pressure or by suction. The resulting low flow rates of tested air, which must be monitored in order to check operability of the detector cannot be determined with the use of the usual measuring and indicating devices. Operability however, may be checked by determining the pressure imminent in each flow motion.
A prior art indicator utilizing the presence of a pressure, such as a .+-. deviation from the gas pressure in breathing apparatus for high altitudes, comprises a cylindrical body which is connected to a diaphragm closing a pressure chamber. The device is provided with a preferably luminous mark and arranged in such a relationship to a conical mirror that in the rest position, the mark is masked by the mirror. At a predetermined pressure, the mark moves into the mirror and becomes visible. Aside from the motion of the diaphragm, the function of the device also requires movement of the cylindrical body. An indicator of such construction is necessarily complicated, particularly if positional independence is wanted (West German Pat. No. 950,693).
Another known pressure indicator, producing an optical signal, is responsive to compressed air and operates by displacing a piston within a compressed air system.
During its displacement, the piston penetrates a yielding, slotted diaphragm extending transversely to the displacement, and causes the areas bounded by the slots to bend. This bending indicates the pressure to be monitored within a system.
To operate, this pressure indicator again needs a movable part, namely the piston and has the same disadvantages of the device above West German Auslegeschrift 20 21 325.